1. Field of the Invention
The present invention relates generally to the fields of blood vessels and of coagulation. More particularly, it embodies the surprising finding that Tissue Factor compositions can localize to tumor vasculature and cause specific coagulation. Methods and compositions for effecting specific coagulation and for treating tumors with modified Tissue Factor (TF) compositions and combinations of TF and other molecules are particularly provided.
2. Description of Related Art
Tumor cell resistance to various chemotherapeutic agents represents a major problem in clinical oncology. Therefore, although many advances in the chemotherapy of neoplastic disease have been realized during the last 30 years, many of the most prevalent forms of human cancer still resist effective chemotherapeutic intervention.
A significant underlying problem that must be addressed in any treatment regimen is the concept of "total cell kill." This concept holds that in order to have an effective treatment regimen, whether it be a surgical or chemotherapeutic approach or both, there must be a total cell kill of all so-called "clonogenic" malignant cells, that is, cells that have the ability to grow uncontrolled and replace any tumor mass that might be removed. Due to the ultimate need to develop therapeutic agents and regimens that will achieve a total cell kill, certain types of tumors have been more amenable than others to therapy. For example, the soft tissue tumors (e.g., lymphomas), and tumors of the blood and blood-forming organs (e.g., leukemias) have generally been more responsive to chemotherapeutic therapy than have solid tumors such as carcinomas.
One reason for the susceptibility of soft and blood-based tumors to chemotherapy is the greater physical accessibility of lymphoma and leukemic cells to chemotherapeutic intervention. Simply put, it is much more difficult for most chemotherapeutic agents to reach all of the cells of a solid tumor mass than it is the soft tumors and blood-based tumors, and therefore much more difficult to achieve a total cell kill. Increasing the dose of chemotherapeutic agents most often results in toxic side effects, which generally limits the effectiveness of conventional anti-tumor agents.
It has long been quite clear that a significant need exists for the development of novel strategies for the treatment of solid tumors. One such strategy is the use of "immunotoxins", in which an anti-tumor cell antibody is used to deliver a toxin to the tumor cells. However, in common with the chemotherapeutic approach described above, this also suffers from certain drawbacks. For example, antigen-negative or antigen-deficient cells can survive and repopulate the tumor or lead to further metastases. Also, in the treatment of solid tumors, the tumor mass is generally impermeable to molecules of the size of the antibodies and immunotoxins. Therefore, the development of immunotoxins alone did not lead to particularly significant improvements in cancer treatment.
Certain investigators then developed the approach of targeting the vasculature of solid tumors. Targeting the blood vessels of the tumors has certain advantages in that it is not likely to lead to the development of resistant tumor cells or populations thereof. Furthermore, delivery of targeted agents to the vasculature does not have problems connected with accessibility, and destruction of the blood vessels should lead to an amplification of the anti-tumor effect as many tumor cells rely on a single vessel for their oxygen and nutrient supplies. Exemplary vascular targeting strategies are described in Burrows et al. (1992), in Burrows and Thorpe (1993) and in WO 93/17715. Such targeted delivery of anti-cellular agents to tumor vasculature provides quite promising strategies, however, the use of the toxin portions of these molecules still leaves room for improvement in vascular targeting.
Another approach for the targeted destruction of tumor vasculature has been reported in WO 96/01653, in which antibodies against tumor vasculature markers are used to deliver coagulants to the vasculature of solid tumors. The targeted delivery of coagulants in this manner has the advantage that significant toxic side effects are not likely to result from any background mis-targeting that may result due to any low level cross-reactivity of the targeting antibodies with the cells of normal tissues. The antibody-coagulant constructs for use in such directed anti-tumor therapy have been termed "coaguligands" (WO 96/01653).
Although the specific delivery of a coagulant to a tumor vessel marks a surprising advance, the use or manipulation of coagulation in connection with treatment of various human diseases and disorders has been practiced for some time. By way of example only, Morrissey and Comp have proposed the use of truncated Tissue Factor (tTF) in combination with Factor VIIa (FVIIa) in the treatment of patients, such as hemophiliacs, in which blood coagulation is impaired (U.S. Pat. Nos. 5,374,617; 5,504,064; and 5,504,067). Roy and Vehar have also developed Tissue Factor mutants that neutralize endogenous Tissue Factor and may be used as anti-coagulants, e.g., in the treatment of myocardial infarction (U.S. Pat. Nos. 5,346,991 and 5,589,363).
In further studies connected with Tissue Factor (TF), Edgington and colleagues have shown that, in contrast to normal melanocytes, malignant metastasizing human melanoma cells express high levels of TF, the major cellular initiator of the plasma coagulation protease cascades (WO 94/28017; WO 94/05328; U.S. Pat. No. 5,437,864). It was reported that inhibition of TF function and subsequent reduction in local protease generation resulted in significantly reduced numbers of tumor cells retained in the vasculature. This led to the suggestion that there was a direct correlation between TF expression and the metastatic phenotype of tumor cells. Edgington and colleagues proposed that a function of TF is required for successful implantation of tumor cells and that interference with TF function, or specific interference with cell surface expression of TF, is useful in inhibiting metastasis. These authors have therefore proposed treating cancer with antibodies directed against Tissue Factor.